The following disclosure will be discussed in terms of a television receiver although it is to be understood that other and further applications and uses are also appropriate. In television receivers, it is a common practice to utilize blanking pulses at the horizontal and vertical scan frequency which are available in the transmitted composite television signal. As is well known, the horizontal blanking pulse is utilized to blank the electron beam of a cathode ray tube or display device intermediate the end of one horizontal scan line and the beginning of another. Similarly, the vertical blanking pulse is employed to blank the cathode ray tube display device during the period required to return the electron beam from the bottom to the top of the display device. Moreover, it is also well known that the horizontal blanking pulse can be employed to provide a black level setting for the signal receiver.
As mentioned above, most television receivers utilize the blanking pulse to provide a desired black level for the signal receiver. Unfortunately, present-day television signals tend to have a varying magnitude which tends to provide an undesired varying blanking pulse and a varying black level as evidenced on the display device or cathode ray tube. Since the variations in black level are deleterious to the viewing pleasure, one approach for improved viewing is the utilization of the maximum video signal rather than the horizontal blanking pulse as a means of determining the black level of the display device.
However, a system which employs a maximum video signal rather than the blanking pulses for determining black level requires removal of the blanking pulse from the received composite signal. Otherwise, the level of the blanking pulses may exceed the level of the video signal whereupon the black level would undesirably tend to be determined by the blanking pulse rather than the video signal level.
Additionally, the composite signal ordinarily employs blanking pulses at both the horizontal and vertical scan frequencies. Also, these horizontal and vertical blanking pulses are vastly different from one another in so far as width and frequency are concerned. Thus, removal of pulse signals of varying frequency and width without deleterious effect on a display device becomes a task of major proportions.